Flame spread and combustion characteristics of straw bales from a point fire source

Combustion experiments were conducted with cylindrical straw bales with various diameters and thicknesses. The flame spread and flame structure were analyzed with a model developed to predict the mass loss rate (ṁ) and flame temperature. The flame structure progresses from a hollow conical flame to a separated annular flame and then a broken annular flame. The mass loss rate first increases and then slowly decreases. The peak mass loss rate is linearly related to the initial straw mass, which implies that a larger initial mass increases the heat accumulation during the straw combustion. The flame temperature distribution along the vertical axis has the same trend as the mass loss rate with the dimensionless flame temperature decreasing slowly with increasing (z-z₀)ṁ^-2/5 for small values of this parameter and then decreasing more quickly at larger values of (z-z₀)ṁ^-2/5. (z-z₀ is the relative flame height.) The conclusions deepen the understanding of straw fire development and spread characteristics.